The present invention refers to a device for carrying-out of the process according to claim 1 of the publication print WO 92/00918, i.e. for creating in an aquifer an oxidation and precipitation zone or a reduction zone between a number of injection wells arranged around one or more extraction wells for purified water, which zone is intended for in situ precipitation or reduction of substances not desired in the ground water, the desired zone being created intermittently between each pair of adjacent injection wells by (i) introducing oxygen, oxygen-containing gas or an oxygen-releasing substance into the water in both wells when creating an oxidation and precipitation zone, or introducing into the water in both wells an oxygen-consuming substance when creating a reduction zone, and (ii) pumping the water in one of the wells from below upwards while pumping the water in the other well from above downwards whereby a circulation circuit is formed in the aquifer between the two wells, said injection wells each comprising an outer tube which at least at the ground-water carrying portion of its length is apertured and water-pervious.
The prior device suggested according to the WO 92/00918 has shown to operate satisfactorily in a number of applications. In some cases where the ground-water has been "troublesome" and severely mingled with contaminants it has turned out that the ejectors have become rather severely clogged such that the process has been slowed down. Particularly the re-directing zones in the gaps between the various tubes have been clogged. The outer tube exhibits only one internal surface in contact with the water while the inner tube is surrounded by the "troublesome" water both internally and externally. In the annular spaces between the tubes there are thus formed deposits both at the outer and inner surfaces so that they will be heavily clogged and the flow restricted. Furthermore, it has turned out to be difficult to flush away or otherwise get rid of said deposits due to the relatively small tube diameter of the injection wells.